A communication system controlling wireless communication includes a network coupled to an exchange and a plurality of base stations coupled to the network. One base station communicates with a plurality of mobile devices.
An area in which communication with a mobile device is ensured owing to one base station is called a cell. It is desirable that the cell covers a whole area in which a mobile device is predicted to move. However, owing to a geographic condition or a communication data amount, an area occurs that may not be covered only by the base station.
In order to supplement the area not covered only by the base station, a relay station is used. The relay station is coupled to the base station. A mobile device, which exists in an area covered by the relay station, accesses the exchange through the relay station, the base station, and the network. A device such as the relay station or the base station, which is located at a network coupling point, is called a node.
In wireless communication in which a communication condition temporally changes, data communication is performed while the measurement value of a radio wave is sent from a mobile device side and a receiving side confirms a communication environment on the basis of the measurement value. When a plurality of nodes exist between the mobile device and the exchange, and a communication distance between relay points is long, a signal propagation delay time between the mobile device and the exchange becomes large. When the signal propagation delay time has become large, confirmation processing for the communication environment with respect to the measurement value becomes delayed. The delay of the confirmation processing results in the deterioration of latency.
In order to avoid the deterioration of latency, there has been a technique in which data communication is performed using independent communication protocols between nodes. Using independent communication protocols between nodes, the sections of data communication individually become short. By shortening the sections of data communication, it may be possible to speed up the confirmation processing for the communication environment with respect to the measurement value.
When a mobile device located in a cell covered by one relay station moves to a cell covered by another base station, handover processing occurs in a communication system so that data communication between the mobile device and the exchange is not disconnected. As related arts, Japanese Laid-Open Patent Publication No. 2010-183645 and Japanese Laid-Open Patent Publication No. 2010-157908 are known.